1. Field of the Invention
The present invention relates to a head control device, a storage device, and a contact detection method that enable a head to come in contact with a storage medium with high precision without causing damage to either the head or the storage device.
2. Description of the Related Art
In magnetic disk devices, a technique of dynamically controlling the distance between the surface of the storage medium, such as a magnetic disk, and the head element (more specifically, the magnetic spacing between the end of the head facing the magnetic disk and the storage medium) is well known (for example, Japanese Patent Application Laid-open No. 2003-272335). According to this technique, a heating element is provided in the head to, cause extension of a portion of the head by heat produced by the heating element to thereby bring the head closer to the storage medium, and the distance between the surface of the storage medium and the head is controlled by controlling the heating value. Controlling the distance between the head and the magnetic disk has become all the more important with the substantial jump in the storage capacity of the magnetic disk devices in recent years.
The storage capacity of the magnetic disk device is increased by increasing the recording density of the magnetic disk. When writing/reading data to/from a magnetic disk having high recording density, the head need to be as close to the magnetic disk as possible to heighten its sensitivity to the signals. However, if the head gets too close to the magnetic disk, there is a risk of the head or the magnetic disk or both getting damaged due to contact with each other.
Accordingly, to enable read/write performance of a high-density magnetic disk device, the head has to be precisely controlled so that the head is maintained very close to the magnetic disk and yet does not come in contact with it. A good precision in control of the head is attained by the thermal expansion described earlier.
To maintain a constant distance between the head and the magnetic disk by control by thermal expansion, a standard floating distance between the head and the magnetic disk needs to be determined. The standard floating distance is determined by controlling the magnetic head by thermal heating so that the head slowly approaches and comes in contact with the magnetic disk, and determining the amount of extension when the head comes in contact with the magnetic disk. The amount of extension can be easily determined by determining the amount of electric current supplied to the heater. Thus, to determine the standard floating distance of the head, the amount of electric current that needs to be supplied to the heater to cause the head to come in contact with the magnetic disk needs to be determined. As a premise to determining the standard floating distance of the head, it has to be accurately ascertained that the thermal expansion of the head has caused the head to come in contact with the magnetic disk.
When coming in contact with the magnetic disk, due to jolt from outside, the head may move away from the target track. A technology to address this issue is disclosed in Japanese Patent Application Laid-open No. 2006-190454, whereby the contact of the head with the magnetic disk is detected based on whether a position error signal has exceeded a threshold limit value.
As the head gets closer and closer to the magnetic disk, the amplitude of the signal read by the head increases. In a technology disclosed in U.S. Pat. No. 4,777,544, the amplitude of the signal read by the head is monitored as the head approaches the magnetic disk, and the contact of the head with the magnetic disk is detected based on whether maximum amplitude is attained.
However, in the method of detecting head-disk contact based on the position error signal, in heads that are steady when floating, the variations in the position error signal are insignificant even when head-disk contact happens, making the head-disk contact detection difficult.
In the method of detecting head-disk contact based on attainment of maximum amplitude by the signal, the amount of electric current supplied to the heater needs to be increased for some time even after head-disk contact has taken place, prolonging the head-disk contact duration.